According to Ancestry.com, Yenser is possibly an Americanized form of German Jenzer or Jentzer, possibly even a variant of Jantzer, a pet name of Johann. Family oral tradition is that it is Pennsylvania Dutch and there is even an article out there with a news item where "Yansers" were gypsies being beaten in New York for sport so the exact origin is yet to be discovered. Most of the Yensers in the United States seem to originate from Pennsylvania and to a smaller degree, Ohio.